Conventional sample analyzers are known to dispense samples such as blood or urine from sample containers to reaction vessels where a sample is mixed with a reagent for use in conducting an intended measurement, and then perform various types of measurements and analyses. The liquids, such as samples and reagents, used in such sample analyzers are stored in predetermined containers and aspirated by an aspirating tube which is inserted into a respective container. There is known art for minimizing the depth of insertion of the nozzle in the liquid to prevent contamination by detecting the liquid level in the container (refer to Japanese Laid-Open Patent Application No. H11-271319).
The art disclosed in Japanese Laid-Open Patent Application No. H11-271319 detects changes in an electrostatic capacity between the liquid and the aspirating tube to detect the liquid level within the container. The art is also configured to have removed static electricity charged on the container to suppress such static electricity from causing an inaccurate detection of the liquid level.
However, there are several factors to be considered other than static electricity that cause an inaccurate detection of the liquid level. For example, in an analyzer, such as the one disclosed in H11-271319, in which the liquid level is detected from detections of changes in electrostatic capacity, conductors such as metal panels and screws provided around the container can act as electrodes to greatly influence readings of the electrostatic capacity, resulting in that detected changes in electrostatic capacity due to travel of the aspirating tube through nearby conductors obscure a reading of the change in electrostatic capacity due to contact with the liquid and make harder the accurate detection of the liquid level. There also is a concern that a liquid level detection may also become inaccurate because of changes in the detected electrostatic capacity caused by a loosened metal screw present around the container and by a replaced metal part. There is further a concern that when liquid level detection is performed by a voltage sensor, a liquid level detection may be inaccurate because of changes in a detected voltage caused by differences in the shapes of containers holding the liquid. Hence, the environment surrounding the liquid level sensor greatly affects the detection signal of the liquid level sensor.